In a parts machining line in which a plurality of robots are arranged, when the type of a work machined by each of the robots is changed, it is necessary to exchange a positioning jig that is prepared for each type of work; thus, there are known conventional robot systems in which, storage units that store jigs are provided at both sides of the machining line, and a carriage on which a jig taken out from one of the storage units is placed is made to circulate in one direction (for example, see PTL 1).